The present invention relates to a technique for recording information onto an optical disk by using a laser beam.
In a rewritable optical disk such as DVD-RAM, DVD-RW, CD-RW and a write once disk such as DVD-R and CD-R, information is recorded by applying a laser beam onto the disk recording surface. As the laser beam application method for forming a recording mark on the recording surface of the optical disk, there is a CD-R method for forming a recording mark by applying a recording pulse having time width according to the length of the recording mark, a DVD-RAM method for making the recording mark forming pulse comb-shape so as to control head accumulation and to form an optimal recording mark, and the like. The waveform of the recording pulse to obtain the optimal recording mark is called write strategy.
FIG. 1 schematically shows a write strategy of 4.7 GB-capacity DVD-RAM (hereinafter, referred to simply as DVD-RAM) which is one of the rewritable optical disks. FIG. 1 shows the write strategy when recording 11T (T is a recording clock cycle) mark. As shown in the figure, the DVD-RAM write strategy consists of a first pulse defined by TSFP, TEFP, TFP, a repeated pulse (multi pulse) defined by TMP, and a last pulse defined by TSLP, TELP, TLP. It should be noted that the laser power level may be binary and tertiary. Here, for simplification, the binary case is shown.
The first pulse of this write strategy may be defined by “a method for defining the waveform rise and fall end absolute time by the TSFP and FEFP” or “a method for defining the rise edge absolute time and the pulse time width by the TSFP and TFP.
Moreover, the last pulse also may be defined by two methods: “a method for defining the edge absolute time by the TSLP and TELP” or “a method for defining the fall edge absolute time and the pulse time width by the TELP and TLP”.
The TSFP which is a value deciding the time position of the front edge of the first pulse and the TELP which decides the time position of the rear edge of the last pulse are varied according to the recording mark length and the preceding and the following space length. This is because affect of the heat accumulation and heat diffusion by the laser beam when recording a mark varies depending on the recording mark length and the preceding and following space length.
FIG. 2 shows an example of adjustment table of TSFP and TELP. The 3T, 4T, 5T, ≧6T (6T or more) arranged in the longitudinal direction of the TSFP table represent the space length immediately before the recording mark while the 3T, 4T, 5T, ≧6T (6T or more) in the lateral direction represent mark length. Similarly, in the TELP table, the 3T, 4T, 5T, ≧6T (6T or more) arranged in the longitudinal direction represent the space length immediately after the recording mark while the 3T, 4T, 5T, ≧6T (6T or more) in the lateral direction represent mark length to be recorded. Since the values in the adjustment table shift the edge of the write strategy decided by TSFT and TELP, hereinafter these tables will be referred to as shift tables. Moreover, values deciding the edge timing of the recording waveform such as TSFP described in FIG. 1 and the aforementioned shift tables will be referred to as recording parameters (parameter group).
The method of modifying the write strategy by the relationship between the recording mark and the space length is used not only in the DVD-RAM but also in the other rewritable phase-change type medium DVD-RW, CD-RW and in the write once type pigment type medium DVD-R, CD-R, and the like.
Conventionally, for the recording parameters, the value which a medium manufacturer considers optimal under the condition of the constant linear velocity is recorded on the medium and provided. Since the write strategy form including the power level and the timing and the optimal values of the recording parameters such as shift tables significantly vary depending on the recording medium composition and material, it has been considered preferable that the medium manufacturer suggest the write strategy. For example, in the DVD-RAM, the aforementioned recording parameters are recorded in the physical format information (PFI) area in the control data zone arranged in the lead in area. It should be noted that the aforementioned conventional technique is disclosed in JP-A-2003-085753 and JP-A-2002-260226.